The present invention relates to a process for testing in situ the compression strength of concretes or the like, and to an automatic apparatus to put the process into practice.
This type of apparatus is particularly used in the building field for testing the compression strength, also referred to as "characteristic strength", of concretes used in forming building structures.
As regards technical rules effective in Italy in the building field, a concrete is individualized on the basis of its characteristic compression strength which is defined as the compression strength value under which 5% of the population of all measured strength values is expected to be found. According to the Italian rules by "characteristic strength" it is meant to designate the strength resulting from compression tests carried out after a lapse of 28 days from the moment of the concrete casting on cube-shaped test pieces.
Therefore, following the traditional method pursuant to the rules presently in force in Italy it is possible to test the characteristic strength of the concrete used in a building only when twenty-eight days have elapsed.
Consequently this method involves the risk that when the concrete has already hardened, due to the result of the compression test the quality of the concrete must be degraded, or strengthening works are required or even the construction must be pulled down.
It is known that an increase in temperature in the case of the concrete represents a hardening accelerating factor, provided that the concrete is kept in a moist environment.
This knowledge is widely used in the industrial field for accomplishing small-sized manufactured articles and precast elements which are allowed to cure in heated environments having a high degree of moisture.
For the purpose, an apparatus has been devised which is the subject matter of the Italian patent application No. 84933/A87. The object of this application is an apparatus comprising: a cure furnace the inner environment of which has adjustable chemico-physical parameters; a transducer adapted to measure the temperature inside the furnace vessel and to emit a signal depending upon the detected value; a device for displaying all data detected by the transducer; a mechanical press adapted to load the test pieces to a predetermined value; a transducer designed to measure the pressure exerted by the mechanical press and emit a signal depending on the detected value; a processor associated with the transducers and capable of instantaneously supplying the value of the compression strength of the concrete and adjusting the temperature value within the vessel. In particular, the furnace and mechanical press in this apparatus consist of two separate devices so that at the end of the cycle an operator is needed for positioning the test piece under the press.
While this apparatus is very precise and reliable, it has the drawback that it needs the presence of an operator at the end of the cure cycle. In fact a cure protracted beyond the stated period modifies the results obtained since only the cure (breakage of the cube) carried out exactly at the end of the cycle can give a result which is the closest to the exact one.